1. Field of the Invention
This invention relates to the testing of integrated circuits or other items having a pattern of contacts thereon, and more particularly concerns a pre-shaped test probe membrane.
2. Description of Related Art
Integrated circuit chips are manufactured with large numbers of identical circuits on a single wafer which ultimately are separately cut from the wafer for use. It is desirable to test each circuit individually to determine whether or not it functions as intended before separating it from the wafer. Additional testing of separated circuits may be desired at various stages in assembly of the circuit in the finished apparatus. Additional testing may be accomplished after packaging a circuit, after placing it in a multi-chip module and after disassembly of a multi-chip module to identify inoperable circuits.
Conventional testing employs a probe card which is provided with a large number of small tungsten blades or needles that are mechanically and electrically connected to a circuit board and act as contacts. Electrical leads extend from the contacts to the outer edge of the board for connecting the probe card to test circuitry. In use the blades or needles are moved into engagement with the pads of an integrated circuit. The motion has to be such that there is a slight scrubbing action that is required for breaking through the oxidation coating that often covers an aluminum integrated circuit chip pad. Thus the blades or needles are frequently positioned at an angle so that they will effectively slide along or scrub a surface of the pad to break the oxide coating. This provides an electrical connection so that signals can be read to determine integrity of the circuit on the chip.
Ends of the needles or blades must all fall in the same plane in order to assure that each one makes electrical contact with a pad of the integrated circuit. This is accomplished by bending the blades or needles after they are mounted on the probe card, which is laborious, time consuming and expensive. Even after such adjustment the blades or needles tend to creep back toward their original position so that their adjusted locations are lost. This loss of adjustment also comes about from the pressure of the needles against the chips, aggravated by the scrubbing action used to assure penetration of the oxide coating. As a result, constant maintenance is necessary or the probe cards will not perform their intended function. Even when in proper adjustment the needles cannot compensate for significant differences in the heights of the contact pads on the integrated circuit chips being tested. The needles also may apply excessive forces against the chip so as to damage the chips. The close spacing necessary for testing some chips cannot be achieved with conventional needle contacts.
Improved testing arrangements are disclosed in a co-pending application Ser. No. 606,676 filed Oct. 31, 1991 by John Pasiecznik, Jr. for Method and Apparatus for Testing Integrated Circuits, and in a co-pending application Ser. No. 07/752,422, filed Aug. 30, 1991 by Blake F. Woith and William R. Crumly for Rigid Flex Circuits With Raised Features as IC Test Probes. Both of these applications are assigned to the same assignee as that of this application, and both are incorporated herein by reference as though fully set forth. In the above-identified application of John Pasiecznik, Jr. a flexible membrane is provided with raised features on one side which connect through circuit traces to a probe card that in turn is connected to the test circuit. During testing use of the probe pressure deflects the membrane to ensure that the contacts of the membrane are pressed against the pads of an integrated circuit to provide an electrical connection.
In the above-identified application of Woith and Crumly a separate pliable soft pad or block of a transparent elastomer is mechanically secured to the membrane to cause part of the membrane to be distended for applying a force between the membrane contacts and the pads of the integrated circuit chip. There is room for improvement, however, in the arrangements of each of these prior applications for assuring that adequate pressure exists between the contacts on the membrane and the pads on the integrated circuit chip to assure good electrical connection, while at the same time avoiding undesirable contact between remaining portions of the membrane and the chip that may be caused by "drape" of the membrane. Additional improvement may be desired in the use of backup devices for shaping the membrane and in the costs of manufacture and use of such backup devices. Although the arrangement of the application of Woith and Crumly improves on the earlier application of John Pasiecznik, Jr. in certain respects, still further improvement is desired in the requirement for use of specially shaped backup members.